Add a search parameter to the LDP container service

[srosset81]

Modify ldp.container.get to accept an (optional) search parameter that would return only those container resources that contain the keyword.

Based on @simonLouvet's request:

{
  SELECT ?s1
  WHERE {
    ?s1 ?p1 ?o1 .
    FILTER regex(str(?o1), “${filter.q}”)
    FILTER NOT EXISTS { ?s1 a ?o1}
  }
}

For the moment, do not make this parameter available via the API.